Electric furnace



K. ERDMANN ELBCTRIC FURNACE Filed Deo' Patented Apr. 18,vv 1939 PATENTOFFICE ELECTRIC FURNACE Konrad Erdmann, 'mensheid Austria, signor toAmerican Magnesium Metals Corporation,

Pittsburgh, Pa.

Application` December ze, 193s, serial No. 118,011

In Austria January 10, 1936 1 Claim.

This invention relates to electric furnaces, and more particularlytoelectrode furnaces, of the type inl which a heating chamber or a mufiiemade from slabs or bricks which are highly refractory but pervious togas, is encased by a heat-insulating material and inserted in a gastightouter casing or shell.

An object of the invention is to provide a furnace in which reactionscan be carried out at vvery high temperatures due to losses through heatconduction being considerably reduced.

Another object of the invention is in an electrode furnace to provide aninsulation aroundy its strengthening members, and this has hitherto beenaccomplished by extending the top of the furnace and if necessary alsothe bottom of the furnace u p to the outer shell. Since refractorymaterials are good heat conductors a heat-conducting connection isprovided in this manner between the muiile and the cold outer shell,which entails very considerable loss of heat. Many an electrothermicprocess, for example the recovery of magnesium from magnesia by heatingan intimate mixture of the material to be reduced with carbonaceousreducing agents cannot therefore be conducted in the known types ofelectrode furnace at as high temperatures as is desirable. When carryingout this reaction in electrode furnaces in which the electrodes areinserted from above uprightly into the furnace chamber there results, inconsequence of heat conduction through the top, the further drawbackthat the temperature in the annular gap around the electrodes falls farbelow the temperature prevailing in the furnace chamber with the resultfor ex- (Cl. lil- 9) bridges across the gap and establishes a conductingconnection between the electrode and the furnace wall.

In accordance with the invention the losses due to heat conduction arevery considerably reduced by virtue of the fact that the wall of theheating chamber or muille is supported against the gas-tight outercasing or shell with the aid of individual struts which traverse theheat-insulating material filling out the space between the mule and theouter shell, this filling material preferably consisting, in a mannerknown per se, of loose material (preferably soot). Since the struts haveno other function than to transmit the thrusting forces from the wallsor also from the'top and bottom of the heating chamber to the outercasing or shell their cross-section may be relatively slight, so thatthe losses due to heat conduction are very considerably less than is thecase with known furnaces in `which the top is extended to the outercasing or shell. Experience has shown that, by virtue cf the describedform of supporting, under otherwise precisely equal circumstances the`temperature in the heating chamber can be increased by about 200 C.Moreover, if the furnace is constructed as an electrode furnace it is inthis way also prevented that a conducting connection between theelectrode and the furnace may occur.,

In electrode furnaces care must be taken to ensure thatcurrent cannot-pass from the electrodes to the heat-insulating material filling outthe space between the heating chamber and the outer shell. In accordancewith the present invention this result is achieved by providing theportion of the electrodes which transverses the heat-insulatingmaterial, with a sleeve consisting of two slidably inter-fitting tubesof refractory material, of which the outer tube is secured to the outercasing or shell while theA inner tube 0 is inserted inthe wall of theheating chamber. In consequence of this feature the mutlie can expandand contract without the casing or shell being subjected to detrimentalstress. The two parts of the electrode sleeve have a tight joint, formedfor instance with the aid of asbestos cord, between them, to preventgases or vapors from passing from the annular space between the.electrode and the sleeve, into the heat-insulating material.

A constructional example of a furnace according to the invention isillustratedfin the accompanying drawing, in which Fig. 1 is averticalsection of the furnace, and Fig. 2 a section on the line 2 2, Fig. 1. I

'I'he closed heating chamber I rests upon the pedestal 2, and is sobuilt up, from refractory materials in the form of slabs and`bricks,that the top and the bottom terminate flush with the side walls. Theside walls are provided at the top with a shoulder 3 and at the bottomwith a shoulder I, so that the thrust of the top arch composed of bricksbecomes transmitted to the side walls and from these latter to thebottom. 'I'he side walls and the bottom are supported against thegas-tight outer shell 1 of metal by means of struts 5 and 6. Accordingto the ccnstructional exampleshown in the drawing the struts areinserted with their inner end in cupped recesses in the side walls andbottom, respectively, and with their outer end in sockets 8 and 9 whichare connected in a suitable manner to the metal shell. If desired, theportion of the metal shell, which takes up the lateral pressure of thesocket-like abutments may be strengthened by means of reinforcements,for example U-section irons I0. 'I'he space between the heating chamberand the metal shell is filled with soot.

The struts 5 and 6, which consist of refractory material, for examplegraphite or the material used for manufacturing carbon blocks, are onlysubjected to compression or to buckling stress, and can therefore bemade relatively thin, so that the amount of heat conducted to theoutside by the struts is small.

The electrodes II, which traverse the shell 1, are led-in through thetop of the heating chamber in a known manner so that between the elec-Ycurrent from the electrode to the top is prevented.

In order to preclude also the possibility of current passing from theelectrodes to the insulat- ISO ing material which surrounds al1 theuwalls of the heating chamber in approximately the same thickness oflayer, the portion of the electrodes which passes through the insulatingmaterial is encased in a tube of refractory material which penetratesthe outer shell and is fitted with its lower end in the top of theheating chamber. In order to allow for the expansion of the heatingchamber this protective sleeve is composed of two slidably inter-ttingand tightly jointed parts, lnamely a short length of tube I3 made fromheat-insulating material which is secured to the outer shell and acarbon tube I4 mounted on the top of the heating chamber and slidable inthe tube I3. The packing of the joint can be effected for example bymeans of asbestos cord Il wrapped around the upper end of the tube Il.The tubular member I3 carries the water-cooled stumng-box I6 cf theelectrode and is provided with an inlet pipe I1 through which anindifferent or reducing gas, for example hydrogen, may be introduced toflush the annular gap between the electrode and the top of the furnace,so that the gaseous and vaporous products of reaction evolved in thefurnace are prevented from entering this gap.

The furnace is charged from below through a flared passage I8 the chargebeing fed by a conveyor screw I9 into a feed pipe 20 from which it ispushed into the passage I8 by means of a piston 2| which is actuated bya crank gear 22. 'I'he gaseous and vaporous products of reaction passthrough an opening 23 in the side wall of the heating chamber intoa'condenser 24.

In the case of furnaces of small dimensions the top of the heatingchamber may be made of a plate, although in this case also struts mustbe provided, so that anylateral compressive forces or thrusts occurringif the plate should crack during the furnace run are transmitted to theouter shell.

According to the provisions of the patent stat'- utes I have explainedthe principle and construction of my invention and have illustrated anddescribed what I now consider to represent its best embodiments.However, I desire to have it understood that within the scope of theappended claim the invention may be practised otherwise than asspecifically illustrated and described.

I claim:

Electric furnace comprising a heating chamber made from refractorymaterial resting on a support for taking up the weight of the chamber,an outer casing surrounding said heating chamber so as to form anintervening space between said casing and said chamber which space isfilled up with heat-insulating material, individual struts beingprovided traversing said space and flllin'g material to carry the thrustfrom the heating chamber to the outer casing, and electrodes passingthrough the top of the outer casing into the heating chamber through asleeve consisting of two interfltting tubes of refractory .materiaL theouter tube being secured to the outer casing and the inner tube insertedin the head of the heating chamber.

, KONRAD ERDMANN.

